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New Revelations on
Driver Head MOI
In case you haven’t heard, the whole reason you’re about to
see the new “square shape" drivers hit the market in 2007 is
the big companies’ effort to offer standard drivers which have
a higher Moment of Inertia, specifically the MOI, that dictates
how much resistance the head will have when impact occurs anywhere
on the toe or heel side of the face. But in this case, even
by using conventional shaped drivers with slightly lower MOI
measurements than the new OEM models, Clubmakers will be able
to offer their golfers a much higher MOI on the drivers they
custom fit.
Whaat? You mean TWGT is coming out with a super high new MOI
driver this year? No, that’s not what we mean. We mean you
have had the ability to custom build drivers in which the head
has a higher MOI than any of the new OEM square drivers for
years – you just didn’t know it. Well, for that matter,
neither did we until we got a little deeper into an R&D project
we have been working on this winter. And man, is this not only
cool, but it puts the big companies who only offer standard
made clubs off the rack in a real second place position to you
when it comes to really offering golfers a driver head with
a higher MOI!
You’re well aware by now that the stock drivers all of the
major brand name companies make and ship to their retailers
are between 45" and 46" in length. We can’t tell you who makes
what lengths in between, but this is the standard length range
for all the big brand name companies’ men’s drivers which are
sold off the rack to millions of golfers every year. As a clubmaker
who works in the world of swingweight and/or MOI of the assembled
club, you should be aware of how much the OEMs driver heads
have to weigh to be able to end up with a D0-D2 swingweight
with their 65-75 gram graphite shafts. That’s right, somewhere
between 188 and 198 grams is what the headweight has to be for
today’s OEM brand name driver heads.
The MOI of a clubhead as measured about the vertical axis through
the center of gravity is now limited under the rules of golf
to a maximum of 5,900 g-cm2 with an additional tolerance of
100 g-cm2. This means any driver with an MOI of 6,000 g-cm2
or lower is OK with the USGA
First a word on g-cm2, the USGA ordained form of measurement
of the MOI. In simple terms, two things cause the MOI to increase
or decrease. First one’s easy. The heavier the clubhead, the
higher the MOI. For proof, look at the array of high MOI “branding
iron style" putter heads that have come on the market in the
past 3-4 years, all trying to achieve a higher MOI than the
one before. There are putter heads in the industry today which
have an MOI in excess of 10,000 g-cm2! Why are the big companies
only able to achieve an MOI in a driver head of 5,000 to 5,250
g-cm2? Headweight, that’s the main reason.
Putter heads with an MOI over 10,000 g-cm2 weigh well over
400 grams. Driver heads, as we just mentioned, weigh between
188 and 198g. At least the heads on the OEM standard made drivers
do. If you are a really smart and good clubmaker, most of the
driver heads on the custom fit drivers you build weigh more
than that.
Why? Because smart Clubmakers fit and build far, far
more drivers at lengths shorter than the OEMs’ standard range
of 45-46" than they do at those OEM standard lengths. TWGT is
firmly convinced that perhaps 80% of all male golfers currently
using a 45-46" driver would hit the ball farther, straighter
and more consistently on center if they were properly custom
fit into a driver that is at least an inch or more shorter than
the OEMs standard driver lengths. Thousands of Clubmakers have
tens of thousands of golfers who enjoy the game more now because
of just that – a shorter driver that is properly swingweighted
or MOI’d for that golfer’s ability.
Here’s how you will continue to build drivers with a higher
head MOI than any of the big companies will offer this year.
The headweight of a driver built in a range from 43.5 to 44"
with the same 65-76g graphite shaft, and 50 gram grip to a swingweight
of D1 will be 205 to 212 grams.
From TWGT’s recent studies, the average increase of the MOI
for the average 460cc driver today when ONE GRAM is added to
the headweight is 35 g-cm2. That means if you fit a golfer into
a driver that is 44" in length with a driver head that has a
starting MOI of 4800 g-cm2, that same head will have an MOI
of 5,220 g-cm2 when you finish building it to a D1 swingweight.
If you built it 43.5" in length, which many, many golfers
need to really improve their driving consistency, the driver
head’s MOI would be 5,430 g-cm2.
Next time some golfer waves his new square driver in front
of you bragging about his 5,000+ MOI, just smile at him and
tell him that you can beat that by several hundred or more!
(And by making th driver a little shorter, you’ll do the things
on the driver the golfer needs to hit the ball farther, straighter,
and more on center than he does now!)
Clubmakers, you have always had an advantage over the competition
from the get-go because you have the ability to custom fit golfers
with the best specifications that will allow each different
golfer to get the most from their size, strength, athletic ability
and swing characteristics. The only difference with this little
revelation about driver head MOI is that you now have a NUMBER
to put in front of your golfers to PROVE that you can make a
better golf club than they can buy off the rack. In a world
that is all too often fraught with marketing hype, you now have
something of scientific fact that might make a little sense
to golfers who are more difficult to convince of your skills.
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Three Scientific
Reasons to go Shorter, Not Longer, with the Driver
Thanks to TWGT’s understanding of the science of clubfitting,
we are pleased to offer Clubmakers some facts of physics in
understandable terms for why so many golfers cannot consistently
hit a standard 45-46" length driver they buy off the rack, and
why they would be better off with a shorter driver length to
get more from their swing ability.
1. Longer Drivers Have Lower
Headweight Which Reduces the Possible Energy the Golfer can
Deliver to Impact with the Ball for any Given Swing Speed
One of the most familiar and basic formulas of physics is E=1/2
mv2, which applies in golf to the line or transfer of energy
from the clubhead to the ball. Energy is equal to one-half the
mass of the clubhead times the velocity the golfer can swing
the clubhead. In short, if the golfer can swing a driver with
a heavier headweight the same speed they can swing a driver
with a lighter headweight, the shot hit with the heavier clubhead
will have a higher ball speed and fly farther.
This is part of the science which explains why golfers could
possibly hit a club with a graphite shaft farther than a club
with a heavier steel shaft. First, by changing from a heavy
steel shaft to a light graphite shaft, the total weight of the
club is lower, which in turn means the golfer should generate
a higher swing speed with the same swing effort. Second, the
headweight in the club built with the light graphite shaft will
be greater for the same swingweight than the headweight in the
club built with a heavier steel shaft. Thus the golfer should
get a two boosts for more distance with graphite shafts over
havier steel shafts – one from the higher swing speed that results
from the lower total weight, and the other from the higher headweight
in the club that is swung at the higher swing speed.
Clubmakers need to realize the second bit of science explained
above can also pertain to shorter length drivers, especially
when swung by less skilled golfers. A 45-46" driver will have
a much lighter headweight at the same swingweight as a shorter
length driver. Typical driver headweight for a 45-46" length
driver is in the range of 188g to 198g. The usual headweight
for a 43.5" to 44" driver will be in the area of 205g to 212g.
Thus if the golfer swings the shorter driver the same speed
as the longer driver, which, when you read point #3 in this
discussion is very likely for many golfers, the shorter driver
will transfer more energy to the ball for the same swing speed
and hit the ball farther.
2. Longer Drivers Have Lower
Headweight Which Reduces the Moment of Inertia of the Driver
Head and Potentially Robs the Golfer of Forgiveness When the
Ball is Hit Off Center
If you took the time to read the technical discussion previous
to this one in this E-TECHreport, you know the science behind
this point #2. The heavier headweight that comes with a shorter
length driver automatically increases the MOI of the driver
head at an approximate rate of 35 g-cm2 for each ONE gram of
headweight increase. Thus, shorter length drivers can offer
even more off center hit forgiveness than will longer length
drivers. 
3. Longer Drivers Increase the
MOI of the Driver in the Full Swing and Put More Load and Stress
on the Golfer Which can Cause the Swing to Break Down and/or
Become less Repeatable
Virtually every teacher of the swing agrees that in a good,
repeating golf swing, the spine remains stable during the backswing,
downswing and finally, though impact with the ball. The spine
is the axis around which you rotate your body and the club in
making a full swing. As such, there is an important Moment of
Inertia that includes the driver plus your hands, arms and shoulders
as all are rotated together around the axis of your spine.
The longer the length of the driver and the farther the driver
head is from the spine during the downswing, the higher this
MOI will be, and from it, the more stress or load will be put
on the golfer as he/she swings the club. How the golfer reacts
in their swing to the greater load of a longer length driver
determines a golfer’s ability to increase swing speed or not
when using a longer length driver. This is a pretty complicated
factor so let’s stop and take a look at a couple of diagrams
to help explain what we mean.
In Diagram #1, we show the position of the club and the hands/arms
in relation to the shoulders and the spine near the end of the
backswing. The dashed line from the spine to the clubhead is
the radius of rotation for the clubhead around the spine’s axis.
MOI is defined as the mass of the club times the square of
the radius of rotation. So the longer that dashed line,
the higher the MOI about the spine axis, and from it, the more
load placed back on the golfer. In addition, the longer the
driver length, the longer the dashed line, so the MOI and load
on the golfer increase when golfers use longer length clubs.
Diagram #2 shows how the dashed line representing the MOI radius
of rotation about the golfer’s spin will be increased when the
golfer unhinges the wrist-cock early in the downswing. The early
release moves the clubhead and its mass farther from the golfer’s
spine, which in turn increases the MOI about the spine and places
more load back on the golfer. In many cases, a longer driver
does cause the golfer to unhinge the wrist-cock angle earlier
than will a shorter driver because of the greateer load put
on the golfer by the higher MOI of the longer length.
In Diagram #3, you can now see the actual difference in the
radius of rotation about the spine for the two different golfers
that comes from an early release.
While a longer length driver will only increase this radius
of rotation slightly, and from it, increase the MOI and load
on the golfer, it is not uncommon for the load from a longer
club to actually cause some golfers to begin to release the
club earlier than they would when using a shorter length club.
In addition, it is not uncommon for the longer length driver
and its greater MOI and load to also cause golfers with the
tendency toward an outside/in swing path to aggravate that unfavorable
swing path even more.
With all this science in mind, the question that still has
to be answered is how do we know what golfers are going to be
ok with a longer length driver and what golfers will not? First
of all, the only possible reason a golfer should think about
using a longer length driver is if they are able to increase
their swing speed while not decreasing 
control
over the club. The only way to do that is to be able to prevent
the dashed line from the spine to the clubhead from increasing
in length until late in the downswing, just before impact. In
other words, golfers who have the ability to hold the wrist
cock angle until late in the downswing, and thereby not increasing
the MOI and load in the downswing, are about the only people
who have the ability to increase swing speed with a longer length
driver.
But at the end of the day, when you think that the average
driver length on the PGA Tour has been 44.5” for the past two
years, and you remember that the standard length of OEM drivers
sold off the rack in retail golf stores is 45-46”, why would
any golfer choose to play with a driver length of 45-46”? Golf
is a game of percentages, and this information offers a pretty
strong case that going shorter for the vast majority of golfers
is going to be better rather than worse for their game and shotmaking
consistency.
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Search Arsenal Expanded
With the release of the second book in the Search series,The
Search for the Perfect Driver, TWGT now has two different
publications all working hard in the consumer market to elevate
the image of custom Clubmakers and the benefits of real custom
fitting. The Search for the Perfect Golf Club, the debut
volume in the Search series, is still selling well in hardback
form and conveying the message to golfers that real custom fitting
is much better than buying standard made clubs off the rack.
There is no question that the sales of the two Search books
through all of the major retail bookselling firms is beginning
to make golfers aware of the services of custom Clubmakers
and the benefits of real custom fitting. But waiting for
the sales of these books to gradually do their job and send
golfers to you to be custom fit is too much of a “reactive”
behavior.
We can’t stress enough to Clubmakers that being “proactive”
with the Search books and the very inexpensive booklet of
excerpts, 12 Myths That Could Wreck Your Golf Game, will
definitely increase the number of sets you fit and build
and will increase your business in custom clubmaking.
By being proactive we mean that all Clubmakers who wish
to increase their business must begin planning NOW for the
2007 season and how you will get the message about custom
fitting out to as many golfers in your area as possible.
If you sit back and wait this season, you may have a handful
of fittings which simply show up as a random result of golfers
in your area finding the Search books and digging up your
name from the phone book or elsewhere. But if you start
planning how to find golfers in your area to be able to
give each a copy of the 12 Myths booklet, you will be pleasantly
surprised how busy you can bethis year.
The best results are going to come from each of you digging
up the schedule for all of the charity golf tournaments
in your area. Visit the golf courses and ask them for a
copy of their 2007 tournament schedule. All charity tournaments
want players, so finding the contact people who run each
event won’t be difficult. Call the tournament director and
tell him/her you want to offer them a free 12 Myths book
for each player in the field. There is no question if you
do this, you will have more business. Hundreds of your fellow
Clubmakers found this out in 2006 and are chomping at the
bit to continue this low cost marketing approach in 2007.
Do it. If you do, it WILL work to increase your
business in custom fitting.
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Join Us on the TWGT
Clubmaker Forum
2007 signals the fourth year of the popular, enjoyable and
very educational TWGT Clubmaker Forum. Housed on our www.twgolftech.com
web site for Clubmakers, the Clubmaker Forum is FREE, safe and
a super way to “meet” fellow Clubmakers from all over the world
who share an interest in custom clubmaking, clubfitting and
learning more about every conceivable aspect of golf equipment.
You do have to register to join. But that’s extremely simple,
safe, and painless and will open up a new world of golf equipment
information and camaraderie that you’ll find very enjoyable.
At present there are 2,900 clubmakers who have joined the TWGT
Clubmaker Forum. When you join, you do not have to post. Of
the 2,900 clubmakers who have registered for the Forum, some
1,200 have posted questions or answers or opinions on over 4,500
different clubmaking topics. So if you don’t want to post, you
don’t have to – you can simply scan and read the information
to your heart’s content and remain anonymous.
One of the best reasons to participate is the fact that the
TWGT Forum does not have any “flamers” or, for lack of a better
term, does not have any “jerks”. Golfing and clubmaking friendships
have been formed from the Forum because it is all about pure
enjoyment and fun.
When you become a part of the Clubmaker Forum, you will join
the nicest group of passionate fellow Clubmakers you will ever
“meet.”
See ya on the Forum this year!!
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